In industrial communication networks of distributed control systems, reliability or availability can be a key issue, because a failing communication network can entail an interruption of the control system eventually leading to a shut down of the controlled industrial process. Therefore, communication network redundancy can be an important feature of all industrial control systems demanding high availability, such as Ethernet based communication with commercial switches or where one of the redundant networks is an existing network like the Internet.
In order to prevent wrong or improper cabling of redundant networks to the ports of a device of the control system, dedicated designs of the plugs for the different networks or a color-coding of cables and plugs to facilitate visual inspection can be envisaged. However, these methods can involve an additional engineering effort, generate additional cost for tailor-made parts, and can be incompatible with commercial off-the-shelf components or already existing communication networks.
Alternatives can rely on an identification of the ports of the device and/or the redundant networks to which the ports are assigned, and include this identification in a message sent through the network. The patent application publication US2004061486 discloses a way of detecting improper cabling in a system having boards within a computer or memory system, which boards are connected by redundant backend networks or communication loops. Messages identifying, by a backend identifier or loop ID, a redundant backend network are spread by a host processor and evaluated in order to determine whether or not all the boards are connected to the same redundant backend network. This method is specific for loop topologies serially interconnecting neighboring boards. The identification of an individual wrongly connected port involves user intervention and starts with an investigation of the nearest board to the host processor signaling a wrong cabling.
Substations in high and medium-voltage power networks include primary devices such as electrical cables, lines, bus bars, switches, power transformers and instrument transformers, which can be arranged in switch yards and/or bays. These primary devices can be operated in an automated way via a Substation Automation (SA) system. The SA system can include microprocessor based, programmable secondary devices, so-called Intelligent Electronic Devices (IED) responsible for protection, control and monitoring of the primary devices. The IEDs can be assigned to one of three hierarchical levels, i.e. the station level, the bay or application level, and the process level being separated from the bay level by a process interface. The station level of the SA system includes an Operator Work Station (OWS) with a Human-Machine Interface (HMI) and a gateway to a Network Control Centre (NCC). IEDs on the bay level, also termed bay units, in turn can be connected to each other and to the IEDs on the station level via an inter-bay or station bus. The communication network connection points of the latter, i.e. the (ports of the) Ethernet switches to which the various application and station level IEDs are connected, can have a relatively short Mean Time To Failure (MTTF). Hence, each IED is connected, via two distinct ports to two distinct and hence redundant communication networks as physical communication channels (managed according to Parallel Redundancy Protocol PRP), or to two distinct switches in a ring configuration (managed e.g. according to Rapid Spanning Tree Protocol RSTP, or to IEC 62439 Media Redundancy Protocol MRP).
In contrast to direct cable connections as in the communication loops mentioned above, communication networks or buses can include a plurality of access points or switches from which cables connect to the devices of the control system, i.e. to their ports and communication circuits. In addition to diagnosing a link between two devices having a wrong cabling that jeopardizes the wanted redundancy, an identification of the exact location (device and port) of an improper connection can be desired. This identification may include an indication if only one port is connected or if both ports are connected to the same network, or if both ports are cross-connected to the wrong networks.